WRF spectral nudging

Use grid_fdda = 2 to turn on spectral nudging. To turn it off, use grid_fdda = 0.

xwavenum and ywavenum determine the wave number. We usually set the “wavelength” to a few hundred kilometers.

&fdda
grid_fdda                           = 0,     0,
xwavenum                            =13,    11,
ywavenum                            = 4,    11,
gfdda_inname                        = "wrffdda_d<domain>",
gfdda_end_h                         = 22206,   22206,
gfdda_interval_m                    = 360,   360,
fgdt                                = 0,     0,
fgdtzero                            = 0,     0,
if_no_pbl_nudging_uv                = 1,     1,
if_no_pbl_nudging_t                 = 1,     1,
if_no_pbl_nudging_ph                = 1,     1,
if_zfac_uv                          = 1,     1,
 k_zfac_uv                          = 50,   50,
if_zfac_t                           = 1,     1,
 k_zfac_t                           = 50,   50,
if_zfac_ph                          = 1,     1,
 k_zfac_ph                          = 50,   50,
guv                                 = 0.0001,     0.0003,
gt                                  = 0.0001,     0.0003,
gph                                 = 0.0001,     0.0003,
if_ramping                          = 0,
dtramp_min                          = 60.0,
io_form_gfdda                       = 2,